A camera module is mainly categorized into fixed focus (FF) type and auto focus (AF) type. The FF type module has one fixed focal distance. The AF type basically has fixed focal distance, but the focal distance can vary when an actuator formed within lens unit is operated by electric current or voltage applied to the lens unit. The AF camera module generally has a lens system including a plurality of lenses, and also includes an actuator such as voice coil motor (VCM) so that the respective lenses can be moved to thus vary relative distances and optical focal distance.
Recent mobile phones are mounted with cameras which enable users to take still or moving images. These cameras keep advancing further, thus providing higher resolution and higher picture quality.
Camera modules mounted on the mobile phones necessarily go through operation tests. To be specific, presence of defect is determined through open/short test, resistance value measurement of electric line, current consumption test, input/output leakage current test, or the like.
Further, before shipment from the factory, the camera module has to go through a fixed focus controlling in which lens unit is precision-rotated to determine fastening depth so that the lens unit is at a specific fixed focal distance with a sensor and a housing, and the camera module also goes through tests such as image test, and AF driving test. The focusing is the process of testing fixed focus of the lens, the image test is the process of precise-analyzing output image of the camera module to find defect in unit pixels within sensor or defects such as scratches or particles, and the AF driving test is the process of inspecting malfunction of automatic focusing by driving a driving unit of the camera module such as VCM.
Conventionally, since different devices are used to conduct the fixed focus controlling, the image test and the AF driving test with respect to the camera module, the process is quite cumbersome.
Further, while it is necessary to descend the collet unit of the focusing chart unit (including minimized optical system to form a virtual distance with the focusing chart with an image) for fixed focus test to control fixed focus with respect to the camera module, the focusing chart unit is relatively heavy and bulky. Therefore, quite complicated driving mechanism is used.
Further, the lens unit of the camera module is oftentimes damaged when the collet unit of the focusing chart unit descends excessively.
Further, regarding AF type camera module, the actuator structure has a drawback in which it is difficult to obtain exact focus measurement due to contact pressure of the collet to the lens unit during fixed focus controlling operation.